1. Field of the Invention
The present invention relates to a warm white light emitting apparatus, and more particularly, to a warm white light emitting apparatus that includes an LED-phosphor combination to generate a base light of white or yellowish white and an LED-phosphor combination to generate light to adjust a Color Rendering Index (CRI) of the base light.
2. Discussion of the Background
A white light emitting apparatus using light emitting diodes (LEDs) as light sources to emit white light have been increasingly developed. An LED includes a junction of p-type and n-type semiconductors, and uses a light emitting semiconductor in which energy corresponding to a bandgap of a semiconductor is emitted in the form of light due to a combination of electrons and holes when voltage is applied thereto.
A white light emitting apparatus to emit white light using LEDs of three primary colors, i.e., red, green, and blue, is known. The white light emitting apparatus, however, may have a complicated circuit configuration, may make it difficult to provide uniform white light due to the difference of distances between the LEDs of the three primary colors, and may not be economically efficient. Further, in the white light emitting apparatus using the LEDs of the three primary colors, color rendering and color reproduction properties of white light may be limited.
FIG. 16 is a Commission on Illumination (CIE) 1931 chromaticity diagram showing full colors of a conventional white light emitting apparatus. Referring to FIG. 16, a triangle region defined by color coordinates of three primary colors used in the NTSC regulations exists on the CIE1931 chromaticity diagram. Light of a white region may be provided depending on a change in slope of a curve according to current applied to red (R), green (G), and blue (B) LEDs in the triangle region. At this time, the white region is shown along a black body locus curve (BBL curve), wherein the slope of the BBL curve increases from infinity to about 4000K and then decreases after it passes through about 4000K, based on x and y axes that are the abscissa and the ordinate, respectively. Therefore, light of a warm white region that is shown along the BBL curve and has an excellent color rendering property may not be provided using only the red, green, and blue LEDs.
There is also known a white light emitting apparatus that emits white light using the combination of a blue LED and a yellow phosphor. Such a white light emitting apparatus advantageously may provide a simple circuit configuration and may be inexpensive. However, its color rendering property may be degraded, and its color production property may be considerably degraded due to a low light intensity in a long wavelength.
Further, there is a conventional white light emitting apparatus that emits white light using the combination of a blue LED and red and green phosphors having different excitation wavelengths. Since the white light emitting apparatus has red, green, and blue peak wavelengths, the white light emitting apparatus has color rendering and color reproduction properties superior to a light emitting apparatus using a yellow phosphor. However, in such a light emitting apparatus, different kinds of phosphors are positioned in an encapsulant without being separated from each other. For this reason, light loss may be high, and efficiency of the phosphors may be degraded.